Method of strengthening binder metal phase of sintered body

ABSTRACT

Spherical shaped ejection particles are ejected against a surface of a sintered body including hard particles and a binder metal phase bonding the hard particles together, with a compressed gas at an ejection pressure of from 0.2 MPa to 0.6 MPa or at an ejection velocity of from 80 m/s to 200 m/s and the spherical ejection particles having a hardness not less than the hardness of the binder metal phase and that is a hardness of 1000 HV or less and being particles having an average particle diameter from 20 μm to 149 μm. Thus, plastic deformation resulting from such impact and the instantaneous temperature rise and cooling occurring at the impact sites micronizes the structure of the binder metal phase, causes a change to a dense structure, and imparts compressive residual stress thereto. This results in strengthening, and enables prevention of brittle fracture in the sintered body.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method for strengthening a phase of abinder metal (referred to as a “binder metal phase” in the presentinvention) in a sintered body in which hard particles of a carbide,oxide, nitride, boride, silicide, or the like are sintered together witha binder metal such as Fe, Ni, or Co, such as in a cemented carbide, acermet, or cBN.

2. Description of the Related Art

Taking an example of a cemented carbide as an example of such a sinteredbody, the cemented carbide is configured by fine particles (normalparticles of cemented carbide have a particle diameter of a few μm, andultrafine particles of cemented carbide have a particle diameter of fromabout 0.5 μm to about 0.8 μm) of a carbide (WC, TiC, TaC) of a metalsuch as tungsten (W), titanium (Ti), Tantalum (Ta) sintered togetherusing as a binder a metal such as iron (Fe), nickel (Ni), or cobalt(Co). As narrowly defined, cemented carbide sometimes refers to onlyWC—Co based alloys configured from particles of tungsten carbide (WC)sintered together using a cobalt (Co) binder.

Such cemented carbides are materials have remarkable hardness, in ahardness range of from 1000 HV to 1800 HV, and excellent wearresistance, and are accordingly employed as the material for tools,machine components, and the like where wear resistance is demanded, suchas cutting tools.

However, although cemented carbides have high hardness, they have thedisadvantage of being brittle, and brittle fracture is liable to occur.This means that, for example, cracks, nicks, and the like are liable tooccur at the cutting-edge of cutting tools made from cemented carbide.This reduces productivity due to the need to either replace cuttingtools partway through a job when such cracks or nicks have occurred, orto perform a regrinding operation or the like to regenerate the cuttingtools cutting-edge.

There is accordingly a desire for the provision of a cemented carbidethat, while having high hardness, also has excellent toughness and isnot susceptible to brittle fracture such as cracks or nicks.

The mechanical characteristics, such as hardness and toughness, ofcemented carbides are known to vary according to the particle diameterof the hard particles and the addition amount of the binder metal.

Accordingly, it might be supposed that the particle diameter of the hardparticles and the addition amount of the binder metal should be changedto obtain a cemented carbide having the targeted hardness and toughness.

However, as illustrated in FIG. 1, the relationships of hardness andtoughness against the particle diameter of the hard particles arerelationships in which the hardness of the cemented carbide increasesbut the toughness decreases as the average particle diameter of the hardparticles decreases, and conversely the fracture toughness increases butthe hardness decreases as the average particle diameter of the hardparticles increases.

Moreover, as illustrated in FIG. 2, the relationships of hardness andtoughness against the addition amount of binder metal are relationshipsin which the hardness of the cemented carbide increases but thetoughness decreases as the addition amount of the binder metal isdecreased, and the toughness of the cemented carbide increases but thehardness decreases as the addition amount of the binder metal isincreased.

The hardness and toughness of the cemented carbide accordingly haveconflicting relationships in that increasing one causes a decrease inthe other. This means that a cemented carbide possessing the twoconflicting properties of having excellent toughness while also havinghigh hardness and is accordingly difficult to obtain by adjusting theparticle diameter of the hard particles and adjusting the additionamount of the binder metal.

Proposed methods to improve toughness without reducing the hardness ofcemented carbides accordingly include, for example: a method of coatinga surface of a base body made from a cemented carbide with a hardcoating layer including a toughened zone of excellent toughness (seeabstract of Japanese Patent KOKAI (LOPI) No. 2000-246509(JP2000-246509A); and a method to raise the fracture toughness of only asurface portion while maintaining the overall hardness of a cementedcarbide, which is achieved by providing a surface layer of a toughnessthat has been raised by increasing the WC particle diameter and/orincreasing the Co concentration at the surface of a cemented carbide(see abstract of Japanese Patent KOHYO (LOPI) No. 2004-514790(JP2004-514790A)).

Note that although not directed toward raising the toughness of asintered body such as a cemented carbide, the inventors of the presentinvention have proposed an instantaneous heat treatment method for ametal article directed toward forming micro-structures, dimples, and thelike on a surface by shot peening. In this instantaneous heat treatmentmethod, substantially spherical shaped shot, having a higher hardnessthan the base material hardness of a workpiece and including three ormore different approximate ranges of grain size lying in a range of from100 grit to 800 grit (average particle diameter: 20 μm to 149 μm), aremixed together and a mixed fluid of the shot combined with compressedair is ejected intermittently, at from 0.1 seconds to 1 second andintervals of from 0.5 seconds to 5 seconds, onto the workpiece. Thisejection is performed at an ejection pressure of from 0.3 MPa to 0.6MPa, at an ejection velocity of from 100 m/s to 200 m/s, and with anejection distance of 100 mm to 250 mm, so as to form numerous randomfine indentations having substantially circular bottom faces and adiameter of from 0.1 μm to 5 μm on the surface of the workpiece (claim 1of Japanese Patent KOKAI (LOPI) No. 2012-135864 (JP2012-135864A)). Notethat an example is described in Japanese Patent KOKAI (LOPI) No.2012-135864 (JP2012-135864A) in which a “carbide” is employed as theworkpiece (see Table 11-1 in Japanese Patent KOKAI (LOPI) No.2012-135864 (JP2012-135864A)).

In the related art described above, in a configuration in which a hardcoating layer including a toughened zone is provided on the surface of acemented carbide, as in the configuration described in Japanese PatentKOKAI (LOPI) No. 2000-246509 (JP2000-246509A), forming the hard coatinglayer provided with the toughened zone of high toughness on the surfacewhile maintaining the hardness of the cemented carbide unaffected,enables toughness to be imparted while maintaining the characteristicsof a cemented carbide i.e. high hardness.

However, this method requires an operation to form the hard coatinglayer provided with the toughened zone on the surface of the cementedcarbide using a method such as physical vapor deposition (PVD), chemicalvapor deposition (CVD), or the like. Forming the hard coating film inthis manner requires extensive investment in equipment etc., such as theneed for a costly vacuum deposition system.

Moreover, the reason high toughness is achieved in this method is that ahard coating film is formed on the surface, and not because thetoughness is increased of the cemented carbide itself, which means thatthe toughness is lost if the hard coating film detaches.

However, a configuration such as that described in Japanese Patent KOHYO(LOPI) No. 2004-514790 (JP2004-514790A), in which a surface layer ofhigh toughness is provided on a cemented carbide by increasing the WCparticle diameter and/or increasing the Co concentration, enables thetoughness to be raised locally for only a surface layer portion withoutlowering the hardness within the cemented carbide.

However, a surface layer having increased WC particle diameter and/orincreased Co concentration in this manner has a hardness that isdecreased as a result of increasing the toughness. The wear resistancethereof is accordingly decreased (see FIG. 1 and FIG. 2), and wearreadily occurs when employed in an application in which direct contactor sliding occurs against other members.

Thus in the treatment described in Japanese Patent KOHYO (LOPI) No.2004-514790 (JP2004-514790A), in cases in which there is a further wearresistant coating film formed on the surface layer described above,preparatory treatment is performed to prevent detachment of the wearresistant coating film (Japanese Patent KOHYO (LOPI) No. 2004-514790(JP2004-514790A), [0001]). However, forming the surface layer in thismanner does not enable both toughness and hardness to be obtained in thecemented carbide itself.

Thus, even though there is a strong desire to impart a cemented carbidewith both hardness and toughness, none of the related art listed aboveis able to provide a solution to such a desire.

Thus the inventors of the present invention have performed diligentinvestigations into what is required to enable the toughness of acemented carbide itself to be raised without forming a hard coating filmor the like as described above.

As a result, the inventors have considered whether the occurrence ofbrittle fracture such as cracks or nicks can be suppressed if the bindermetal phase can be strengthened at least in the vicinity of the surfaceof a cemented carbide 1.

Namely, as illustrated in FIG. 3, the cemented carbide 1 has a structurein which hard particles 10, such as WC, are bonded together by a bindermetal phase 20, such as Co, having a higher ductility than that of thehard particles 10.

The hard particles 10 therein have extremely high hardness, for example1780 HV for WC, 3200 HV for TiC, and 1800 HV for TaC, and hardly deform.Any plastic deformation occurring when an external force is imparted tothe cemented carbide 1 can accordingly be logically inferred to haveoccurred mainly in the portion where the binder metal phase 20, such asthe Co, is present. This provides support as to why the overalltoughness (deformability) of the cemented carbide 1 is raised byincreasing the addition amount of the binder metal (see FIG. 2).

In this manner, the deformation of the cemented carbide 1 is thought tomainly occur in the binder metal phase 20 portion, and brittle fracture,such as cracks or nicks occurring in the cemented carbide 1, is thoughtto be generated by cracking of the binder metal phase 20 due to strainaccompanying deformation, which grows as more strain is imparted, andwhich eventually leads to fracturing occurring.

Following on from the above prediction, if the binder metal phase 20portion of the cemented carbide 1 could be strengthened, and inparticular the binder metal phase 20 in the vicinity of the surface ofthe workpiece where fractures tend to originate could be strengthened,then this should enable the ability to withstand brittle fracture suchas cracks or nicks, namely the fracture toughness, to be raised.

Moreover, strengthening the binder metal phase 20 is thought tocontribute to making brittle fracture less liable to occur and toraising the toughness of a sintered body, not only for the cementedcarbide 1, but also for sintered bodies in general having a similarstructure of the hard particles 10 bonded together with the binder metalphase 20, such as a cermet, cBN, or the like.

Note that Japanese Patent KOKAI (LOPI) No. 2012-135864 (JP2012-135864A)discloses an instantaneous heat treatment method performed by ejectingbeads made from high-speed steel (HSS) onto a treatment subject for anExample of a draw punch made from cemented carbide (Table 11-1 ofJapanese Patent KOKAI (LOPI) No. 2012-135864 (JP2012-135864A)).

However, Japanese Patent KOKAI (LOPI) No. 2012-135864 (JP2012-135864A)is significantly different from the present invention in that anessential element is that such treatment should be performed withejection particles harder than the treatment subject (claim 1 ofJapanese Patent KOKAI (LOPI) No. 2012-135864 (JP2012-135864A)).

Moreover, Japanese Patent KOKAI (LOPI) No. 2012-135864 (JP2012-135864A)includes the advantageous effects of increasing hardness bymicronization of the surface structure using the instantaneous heattreatment method, and preventing seizing and the like by dimples formedthereby functioning as oil reservoirs. There is also a reference to“wear resistance” being increased, however there is no referencewhatsoever to raising the ability to withstand nicking and cracking suchas chipping, called “brittle fracture”, namely no reference whatsoeverto increasing toughness.

Following on from the prediction by the inventors, the present inventionis directed towards solving the disadvantages in a sintered body such asa cemented carbide mentioned above of low fracture toughness, andproposes a method to strengthen the binder metal phase 20 in thevicinity of the surface of the sintered body 1 using a comparativelysimple method. An object of the present invention is to make brittlefracture less liable to occur (to impart toughness) while maintainingthe characteristic high hardness of sintered bodies, such as cementedcarbides, cermets, and cBN.

SUMMARY OF THE INVENTION

The following description of means for solving the problem is appendedwith reference signs employed in embodiments for implementing theinvention. These reference signs are employed to clarify correspondencebetween the recitation of the scope of patent claims and the descriptionof embodiments for implementing the invention, and obviously do notlimit the interpretation of the technological scope of the presentinvention.

In order to achieve the object of the present invention, in a method ofstrengthening a binder metal phase of a sintered body, the method ofstrengthening a binder metal phase 20 of a sintered body 1 comprises:

ejecting spherical shaped ejection particles 30 against a surface of asintered body 1 such as cemented carbide that includes hard particles 10such as tungsten carbide (WC) and a binder metal phase 20 such as cobalt(Co) bonding the hard particles 10 together, by ejecting the sphericalshaped ejection particles 30 together with a compressed gas at anejection pressure of from 0.2 MPa to 0.6 MPa or at an ejection velocityof from 80 m/s to 200 m/s and the spherical ejection particles 30 havinga hardness that is not less than the hardness of the binder metal phase20 and that is a hardness of not more than 1000 HV and being particlesof from 100 grit to 800 grit (having an average particle diameter offrom 20 μm to 149 μm).

In the strengthening method, a sintered body 1 employed as a treatmentsubject is a sintered body 1 having a hard coating film (not illustratedin the drawings) coated on at least a portion of surface at a thicknessof not more than 5 μm, and the ejection particles 30 may be ejectedagainst the sintered body 1 at the portion of the surface coated withthe hard coating film.

Moreover, the ejection particles 30 may be any of metal particles,ceramic particles, or a mixture of metal particles and ceramicparticles, and a hardness of the ceramic particles employed ispreferably not more than 800 HV.

EFFECT OF THE INVENTION

The following significant advantageous effects can be obtained bystrengthening the binder metal phase 20 of the sintered body 1 using theconfiguration of the present invention and the method of the presentinvention as described above.

Ejection particles 30 ejected against the surface of the sintered body 1impact the surface of the sintered body 1. The sintered body 1 isconfigured by the hard particles 10 made from WC, TiC, or TaC, and bythe binder metal phase 20 such as a Co phase bonding between the hardparticles 10 (see FIG. 3).

The hard particles 10, such as WC (1780 HV), TiC (3200 HV), or TaC (1800HV), have higher hardness than the ejection particles 30, which have ahardness of not more than 1000 HV. When the ejection particles 30 havinga hardness not less than the hardness of the binder metal phase 20impact the surface of the sintered body 1 serving as the workpiece, asillustrated in FIG. 4B, although there is no deformation of the hardparticles 10 in the sintered body 1, the binder metal phase 20 presentbetween the hard particles 10 undergoes plastic deformation and movesthe hard particles 10, causing the surface of the sintered body 1 todeform.

Plastic deformation resulting from such impact and the instantaneoustemperature rise and cooling (instantaneous heat treatment) occurring atthe impact sites micronizes the structure of the binder metal phase 20in the vicinity of the surface of the sintered body 1, causes a changeto a dense structure, and also imparts compressive residual stressthereto. This results in strengthening.

In this manner, the method of the present invention enables the bindermetal phase 20 in the vicinity of the surface of the sintered body 1 tobe strengthened, and enables good prevention of the occurrence ofbrittle fracture such as cracks or nicks in the sintered body 1, whicharise from cracking and breaking occurring at the grain boundaries ofthe hard particles 10.

Strengthening the binder metal phase 20 in this manner may be similarlyperformed in cases in which a hard coating film (not illustrated in thedrawings) of 5 μm or less is formed on the surface of the sintered body1, enabling the binder metal phase 20 of the sintered body below thehard coating film to be strengthened even after the hard coating filmhas been formed on the surface of the sintered body 1.

Moreover, the cohesion strength of the hard coating film can beincreased and detachment made less liable to occur by strengthening thebinder metal phase 20 in this manner.

Moreover, the micronization and densification occurring in the structureof the binder metal phase 20, and the compressive residual stress thathas been imparted thereto by the ejection of the ejection particles 30might be lost by heating the sintered body 1. Thus film forming of thehard coating film by a method involving heating the sintered body 1 isnot able to be performed after the binder metal phase 20 has beenstrengthened by ejecting the ejection particles 30. However, thesintered body 1 after film forming a hard coating film in this mannercan be employed as the treatment subject, and so this does not provide alimitation to the method of forming the hard coating film.

Furthermore, metal particles, ceramic particles, and a mixture of bothmetal particles and ceramic particles may all be employed as theejection particles 30. In cases in which ceramic particles are employed,making the hardness of such ceramic particles not more than 800 HVenables the toughness to be increased more certainly.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become understood fromthe following detailed description of preferred embodiments thereof inconnection with the accompanying drawings in which like numeralsdesignate like elements, and in which:

FIG. 1 is a graph to explain relationships of hardness and toughness ofa cemented carbide against particle diameter of hard particles therein;

FIG. 2 is a graph to explain relationships of hardness and toughness ofa cemented carbide against addition amount of binder metal therein;

FIG. 3 is a schematic diagram to explain a structure of a sintered body(a WC—Co based cemented carbide); and

FIG. 4 is an explanatory diagram of states of deformation arising whenejection particles have impacted a workpiece of higher hardness than theejection particles, FIG. 4A is for a general workpiece other than asintered body, and FIG. 4B is for a sintered body workpiece including abinder metal phase having a hardness not more than the hardness of theejection particles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Explanation follows regarding a method of the present invention tostrengthen a binder metal phase 20 of a sintered body 1.

Treatment Subject

In the present invention, a sintered body configured by the hardparticles 10 sintered together with a binder metal is employed as atreatment subject. The hard particles 10 are not limited to being asingle type of hard particle, and plural types of hard particle may bemixed together and employed therefor. Similarly, the binder metal isalso not limited to being a single type of metal, and an alloy may beemployed therefor.

Examples of such a sintered body 1 include a cemented carbide, a cermet,and cBN. All of these have a structure such as that schematicallyillustrated in FIG. 3 in which the hard particles 10 are bonded togetherby the binder metal phase 20.

The “cemented carbide” of the sintered body 1 is configured by the hardparticles 10 made from a carbide (WC, TiC, TaC) of a metal such astungsten (W), titanium (Ti), Tantalum (Ta) sintered together with abinder of a metal such as iron (Fe), nickel (Ni), or cobalt (Co). Asnarrowly defined, cemented carbide sometimes refers to only a WC—Cobased alloy of particles of tungsten carbide (WC) sintered togetherusing a binder of cobalt (Co). The present invention is not limited to aWC—Co based alloy, and a cemented carbide containing any of the abovecarbide particles may be employed as the treatment subject.

Moreover, such WC—Co based alloys encompass, in addition to a WC—Coalloy, alloys containing carbide particles other than WC, such as aWC—TiC—Co alloy, a WC—TiC—TaC(NbC)—Co alloy, or a WC—TaC(NbC)—Co alloy.Moreover, the binder metal is not limited to being a single metal suchas Fe, Ni, or Co, and another metal such as an alloy of these metals mayalso be employed.

The “cermet” of the sintered body 1 is a sintered body configured by thehard particles 10 of a ceramic such as a carbide, oxide, nitride,boride, or silicide, bonded together with a binder metal, and within awide definition may include the cemented carbides listed above.

Examples of such cermets include a TiC—Mo—Ni cermet, and also a TiCbased cermet with the addition of TiN, TaN thereto, an A1 ₂O₃—Cr cermet,and the like. Any of these may be employed as the treatment subject ofthe present invention.

Furthermore, the “cBN” of the sintered body is a sintered body of hard(fine) particles 10 of cubic boron nitride of which hexagonal boronnitride is modified by ultrahigh pressure and high temperature, that issintered using a binder metal such as Co.

The sintered body 1 may be employed in various forms and applications,such as in cutting tools such as a milling cutter or drill, shapingtools such as a wire drawing die or a centering tool, wear resistantcomponents such as a roller, gage or dot pin of a printer, acorrosion-resistant tool in a mining application such as a rock cutteror coal cutter, as well as a mold or the like. These may variously beemployed as the treatment subject, irrespective of form and applicationthereof.

Moreover, the above tools and components do not need to be formedentirely of a sintered body, and, for example, a sintered body may beattached to a portion of the tool or component, such as in a cuttingtool or the like in which, for example, a sintered body is attached asthe cutting-edge portion alone by brazing.

Moreover, the treatment subject may be a sintered body in which thesurface of the sintered body serving as the treatment subject has a hardcoating film (ceramic coating film) of, for example, TiN, TiCN, TiAlN,DLC, TiCrN, CrN, or the like formed thereon at a film thickness of notmore than 5 μm by physical vapor deposition (PVD) or chemical vapordeposition (CVD).

Note that for cases in which attachment by brazing or hard coating filmforming accompanied by heating is performed, then such treatment ispreferably completed on the sintered body 1 prior to performing thestrengthening method of the present invention, since the advantageouseffects of strengthening by the micronization and densification ofstructure, imparting of compressive residual stress to the binder metalphase 20, and the like, are sometimes lost if heat is applied after thetreatment by the method of the present invention.

Treatment Content

Dry ejection of the ejection particles 30 together with compressed gasis performed on the surface of the sintered body 1 serving as the abovetreatment subject.

There is no particular limitation to the material employed for theejection particles 30 as long as the material lies within the hardnessrange described below. As well as the ejection particles 30 being madefrom a metal, those made from a ceramic (including glass) may also beemployed. Moreover, not only ejection particles 30 made from a singletype of material, but also ejection particles 30 made from a mixture ofplural materials may also be employed.

The objective of ejecting the ejection particles 30 is to performmicronization and densification of the structure by plasticallydeforming the binder metal phase 20, and to impart compressive residualstress and the like thereto, i.e. the objective thereof is to obtain theadvantageous effects of what is referred to as “shot peening”, and sospherical shaped (spherical shaped particles) are employed therefor.

Note that reference to “spherical shaped” in the present invention neednot refer strictly to a “sphere”, and includes a wide range ofnon-angular rounded shapes, such as spheroid shapes or barrel shapes.

Such spherical shaped ejection particles 30 may be obtained by anatomizing method for metal based materials, and may be obtained bycrushing and then melting for ceramic based materials.

The hardness of the ejection particles 30 employed is a hardness notless than the hardness of the binder metal phase 20 and ejectionparticles of not more than 1000 HV are employed. Moreover, when theejection particles 30 are ceramic particles, then preferably those ofnot more than 800 HV are employed therefor.

For example, the respective melting points for Co, Mo, Ni that may beemployed as the binder metal are 1495° C., 2625° C., 1455° C. Sinteringis performed at a high temperature in the vicinity of the melting pointof the binder metal, and a hardness of the binder metal phase 20 aftersintering is from 500 HV to 800 HV (for example, about 500 HV for Ni,and about from 700 HV to 800 HV for Co).

Thus for the sintered body 1 having a Co phase as the binder metal phase20, alumina-silica beads (792 HV), HSS beads (1000 HV), or the like arefor example suitably employed as the ejection particles 30. However, forthe sintered body 1 having a Ni phase as the binder metal phase 20,preferably glass beads (565 HV) are employed as the ejection particles30.

Note that in cases in which the same metal is employed as the binder,differences in the hardness of the binder metal phase 20 arise accordingto the sintering conditions (heating temperature, pressure, etc.), andso the hardness of the ejection particles 30 is selected based on therespective hardness of the binder metal phase 20.

In cases in which the hardness of the binder metal phase 20 is notknown, for example, trials are performed, in which plural types ofejection particles 30 of different hardness of not more than 1000 HV areactually ejected against the surface of the sintered body 1. Theejection particles 30 capable of rendering a matt (or satin) finish onthe surface of the sintered body 1 in such trials may then be employedas ejection particles 30 having a hardness not less than that of thebinder metal phase 20.

Note that even in cases in which ejection particles 30 having a hardnessof not more than 1000 HV are employed, sometimes considerable damage isinflicted on the surface of the sintered body 1 and the toughnessthereof is actually lowered when ceramic based (including glass)ejection particles 30 with a hardness exceeding 800 HV thus toughnessare lowered. Thus ejection particles 30 having a hardness of not morethan 800 HV are preferably employed for ceramic based ejection particles30.

Furthermore, the ejection particles 30 employed have a particle diameterin the range of from 100 grit to 800 grit for grain size distributionsas defined by JIS R 6001(1987) (an average particle diameter of from 20μm to 149 μm). As long as the particle diameter falls within this grainsize range, a mixture of plural types of ejection particles 30 ofdifferent particle diameter may be employed.

The method for ejecting such ejection particles 30 against the sinteredbody 1 which is the workpiece may employ various known dry type blastingtreatment apparatuses capable of ejecting particles, and an air blastingtreatment apparatus is preferably employed therefor because this enablescomparatively easy adjustment of ejection velocity and ejectionpressure.

Various examples of such air blasting treatment apparatuses includedirect pressure type, gravity suction type, and other types of blastingtreatment apparatus. Any of these types of blasting treatment apparatusmay be employed, and the type thereof is not particularly limited aslong as the blasting treatment apparatus has the performance capable ofejecting the ejection particles at an ejection pressure of from 0.2 MPato 0.6 MPa, or at an ejection velocity of from 80 m/sec to 200 m/sec.

Advantageous Effects Etc.

In the above manner, ejecting the ejection particles 30 and causing theejection particles 30 to impact the surface of the sintered body 1enables the sintered body 1 to be improved by making brittle fracturenot liable to occur and by achieving excellent toughness properties.

Although the mechanism by which such advantageous effects are obtainedis not entirely clear, it is thought that strengthening the binder metalphase 20 in the following manner enables the toughness to be raisedwithout decreasing the hardness of the sintered body 1.

Namely, in cases in which the ejection particles 30 of lower hardnessthan the workpiece are ejected against the workpiece and the workpieceis an ordinary workpiece rather than a sintered body, then normallyplastic deformation as illustrated in FIG. 4A occurs when the ejectionparticles 30 impact, with the plastic deformation mainly occurring onthe side of the ejection particles 30 of lower hardness.

As a result, when ejection particles 30 of lower hardness than theworkpiece are employed, the surface of the workpiece is not able to beplastically deformed, and the advantageous effects that accompanyplastic deformation, of micronization and densification of structure,imparting of compressive residual stress, and the like, are not able tobe imparted to the workpiece.

However, in a sintered body 1 having a structure in which the hardparticles 10 are bonded together by the binder metal phase 20, forexample a WC—Co cemented carbide, although the hardness of the WCparticles configuring the hard particles 10 is a high hardness of 1780HV, the hardness of the Co phase configuring the binder metal phase 20is about 700 HV, giving a combined overall hardness of about 1450 HV.

Thus although the hardness of the ejection particles 30 of not more than1000 HV is a hardness lower than the overall hardness of the sinteredbody 1 (hardness of the WC—Co based cemented carbide: 1450 HV) and lowerthan the hardness of the hard particles 10 (hardness of the WCparticles: 1780 HV), the hardness of the ejection particles 30 is notless than the hardness of the binder metal phase 20 (hardness of the Cophase: 700 HV).

Moreover, the average particle diameter of the hard particles in thesintered body 1 is generally a few μm or so, and for fine hard particlesis from about 0.5 μm to about 0.8 μm, and this is sufficiently smallerthan the particle diameter of the ejection particles 30 at from 100 gritto 800 grit (an average particle diameter of from 20 μm to 149 μm).

As a result, when the ejection particles 30 are caused to impact thesurface of the sintered body 1, as illustrated in FIG. 4B, even thoughno deformation can be achieved of the hard particles 10 having a higherhardness than the ejection particles 30, the hard particles can be movedby deforming the binder metal phase 20, and this is thought to deformthe surface of the sintered body 1 so as to enable processing to aslight matt finish.

Moreover, at the sites impacted by the ejection particles 30, localizedheating and cooling instantaneously occurs at the impact sites due tothe heat generated when impact occurs, and this is thought to result infine crystallization of the binder metal phase 20 by the instantaneousheat treatment performed thereby.

As a result, work hardening by the fine crystallization anddensification is accordingly thought to be induced in the binder metalphase 20, at least in the vicinity of the surface of the sintered body1, with the hardness thereof raised thereby. Moreover, the binder metalphase 20 is thought to be strengthened by being imparted withcompressive residual stress that suppresses the generation and growth ofcracks.

Such strengthening of the binder metal phase 20 is not only obtained incases in which the ejection particles 30 are caused to directly impactthe surface of the sintered body 1, and is also obtained in cases inwhich the ejection particles 30 are caused to impact a sintered body 1having a hard coating film (not illustrated in the drawings) such as aceramic coating film or the like coated on a surface thereof, byimpacting from above the hard coating film. The cohesion strength of thehard coating film is improved thereby, enabling detachment etc. thereofto be made less liable to occur.

It is thought that as a result, by suppressing breaks (breaks in thebinder metal phase 20) at the grain boundaries of the hard particles 10,brittle fracture is less liable to occur even when external force andstrain is imparted to the sintered body 1, and the toughness of thesintered body 1 can accordingly be increased.

EXAMPLES

Next explanation follows regarding results of durability tests onsintered bodies subjected to strengthening of the binder metal phasewith the method of the present invention.

Test Example 1: Cold Forging Punch (Carbide) (1) Test Method

Ejection particles were ejected under the conditions listed in Table 1below against a cold forging punch (diameter 20 mm, length 150 mm) madefrom a WC—Co cemented carbide (1450 HV).

The hardness of the Co phase that is the binder metal phase isapproximately 700 HV.

TABLE 1 Comparative Comparative Treatment Conditions Example 1 Example 1Example 2 Blasting Device Gravity Type Gravity Type Gravity TypeEjection Material HSS (SKII) Glass FeCrB particles HardnessApproximately 534 HV Approximately 1000 HV 1200 HV Average particleApproximately Approximately Approximately diameter 40 μm 40 μm 40 μmShape Substantially Substantially Substantially spherical shapedspherical shaped spherical shaped Ejection Pressure 0.6 MPa 0.6 MPa 0.6MPa conditions Nozzle 9 mm diameter - 9 mm diameter - 9 mm diameter -diameter long long long Ejection 100 mm to 100 mm to 100 mm to distance150 mm 150 mm 150 mm Ejection Approximately Approximately Approximatelyduration 30 seconds 30 seconds 30 seconds

The state of the surface of cold forging punches was observed with thenaked eye after ejection of the ejection particles and on anun-processed cold forging punch. Each of the cold forging punches ofExample 1 and Comparative Examples 1 and 2 was employed to performrepeated cold forging (punching 20 mm diameter holes), and the number ofcycles (shot number) at the time when chipping (nicking) occurred in therespective cold forging punch was employed to evaluate the lifespan ofthe cold forging punch.

(2) Test Results

The test results of Test Example 1 are illustrated in Table 2 below.

TABLE 2 Comparative Comparative Example 1 Example 1 Example 2Unprocessed (HSS) (Glass) (FeCrB) Surface Smooth Slight matt Smooth Mattstate finish (no change) finish No. of punches 30,000 90,000 30,00020,000 (lifespan) (no change)

(3) Interpretation

The above results enabled confirmation that in Example 1, employingejection particles of 1000 HV which is a higher hardness than thehardness of the Co phase (approximately 700 HV), deformation was inducedof the surface of the treatment subject to give a slight matt finish,and a lifespan of three times the untreated case was achieved.

However, in the Comparative Example 1 employing ejection particles of534 HV which is a lower hardness than the hardness of the Co phase(approximately 700 HV), the surface state of the treatment subject wasnot changed and remained smooth, and there was also hardly any change inthe lifespan compared to the untreated case.

Furthermore, in the Comparative Example 2 employing ejection particlesof 1200 HV i.e. higher hardness than the hardness of the Co phase(approximately 700 HV) and also a higher hardness than the ejectionparticles of Example 1, although plastic deformation was induced in thesurface of the treatment subject and a matt finish could be achieved,the lifespan actually reduced relative to the untreated case.

The ejection particles made from HSS employed in Example 1 had ahardness of approximately 1000 HV and a lower hardness than the hardnessof the cemented carbide (1450 HV) of the material configuring the coldforging punch serving as the treatment subject. Thus for the case of anordinary workpiece as the treatment subject, deformation occurring atthe time of impact of the ejection particles would occur at the ejectionparticle side having lower hardness, and as a result hardly any plasticdeformation would be induced on the treatment subject side (see FIG.4A). The advantageous effects of micronization and densification of thesurface structure of the workpiece, imparting of compressive residualstress, and the like would accordingly not be obtained.

However, the sintered body 1 serving as the treatment subject in thepresent invention, as illustrated in FIG. 3, has a structure in whichthe WC particles 10 of high hardness, i.e. 1780 HV, are bonded togetherwith the Co phase 20 having a lower hardness of approximately 700 HV.This means that even when ejection particles having a lower hardnessthan the overall hardness (1450 HV) of the sintered body (carbide tool)are employed as the ejection particles 30, due to employing ejectionparticles of the hardness of the Co phase 20 (approximately 700 HV) orgreater, as explained with reference to FIG. 4B, although the impact ofthe ejection particles 30 is not able to deform the WC particles 10, theCo phase 20 bonding the WC particles 10 together is deformed, moving theWC particles 10. This enables the surface of the sintered body 1 to bedeformed, and the Co phase 20 to be strengthened by forming finecrystals and imparting compressive residual stress accompanying suchdeformation. This is thought to be the reason improvements can beachieved in making brittle fracture, such as chipping and the like, lessliable to occur, and in imparting excellent toughness characteristics.

However, in the Comparative Example 1 employing the ejection particles30 of lower hardness than the Co phase, plastic deformation of the WCparticles is obviously not achieved, and plastic deformation of the Cophase is also not achievable. This is thought to be why, as a result, nochange was obtained in both appearance and lifespan compared to theuntreated case.

Furthermore, in Comparative Example 2 employing the ejection particleshaving a hardness of 1200 HV i.e. a lower hardness than the sinteredbody 1 but a higher hardness than the Co phase, plastic deformation canbe induced in the Co phase. This could be confirmed in the test resultsillustrated in Table 2 by a change of the surface of the sintered bodyto a matt finish.

However, in the sintered body 1 treated under the conditions ofComparative Example 2, a reduction in the lifespan was confirmedrelative to the untreated case, and brittle fracture, such as chipping,was confirmed to actually be more liable to occur.

This confirmed that ejection particles having a hardness of not lessthan the hardness of the binder metal phase (Co phase) need to beemployed as the ejection particles in order to increase the toughness ofthe sintered body (cemented carbide), and that ejection particles havinga lower hardness than 1200 HV, and more specifically preferably employedejection particles have a hardness of not more than 1000 HV such asthose confirmed to strengthen the Co phase in Example 1.

Test Example 2: Header Processing Die (Carbide)

Ejection particles were ejected under the conditions listed in Table 3below against a header processing die (outer diameter 50 mm, innerdiameter 15 mm, height 30 mm) made from a WC—Co cemented carbide (1150HV).

Note that the hardness of the Co phase that is the binder metal phase isapproximately 700 HV.

TABLE 3 Treatment Conditions Example 2 Blasting Device Gravity TypeEjection Material HSS (SKII) particles Hardness Approximately 1000 HVAverage particle Approximately diameter 40 μm Shape Substantiallyspherical shaped Ejection Pressure 0.5 MPa conditions Nozzle diameter 9mm diameter - long Ejection distance 100 mm to 150 mm Ejection durationApproximately 40 seconds

The state of the surface of the header processing die was observed withthe naked eye after ejection of the ejection particles 30. Anun-processed header processing die, and the header processing dietreated under the above conditions (Example 2), were each employed toperform repeated header processing (cold heading) of SCM435, and thenumber of cycles (shot number) at the time when damage occurred on theinner peripheral face of the die was employed to evaluate the lifespanof the respective header processing die.

(2) Test Results

The test results of Test Example 2 are illustrated in Table 4 below.

TABLE 4 Unprocessed Example 2 Surface state Smooth Slight matt finishNo. of cycles 300,000 900,000 (lifespan)

(3) Interpretation

The above results enabled confirmation that in Example 2 employingejection particles having a hardness of 1000 HV, which is a higherhardness than the hardness of the Co phase (approximately 700 HV),plastic deformation was induced of the surface of the treatment subjectto give a slight matt finish. The lifespan was also able to be extendedto three times that of the untreated case. Employing the ejectionparticles within the hardness range stipulated by the present inventionwas confirmed to be effective in increasing the toughness of thesintered body.

Test Example 3: Drill (Carbide) (1) Test Method

Ejection particles were ejected under the conditions listed in Table 5below against a drill (5 mm diameter) made from a WC—TiC—TaC—Co cementedcarbide (91.5HRA (1600 HV)).

Note that the hardness of the Co phase that is the binder metal phase isapproximately 700 HV.

TABLE 5 Comparative Treatment Conditions Example 3 Example 3 BlastingDevice Fine powder Fine powder suction type suction type Ejectionparticles Material Alumina-silica Zirconia-Silica Hardness 792 HVApproximately (Approximately 1000 HV 800 HV) Average particleApproximately <50 μm diameter 38 μm Shape Substantially Substantiallyspherical shaped spherical shaped Ejection Pressure 0.4 MPa 0.6 MPaconditions Nozzle 7 mm diameter - 7 mm diameter - diameter long longEjection 100 mm to 100 mm to distance 150 mm 150 mm EjectionApproximately Approximately duration 20 seconds 20 seconds

Holes were bored in ductile cast iron (FCD400) using the drills that hadbeen subjected to ejection of the ejection particles.

(2) Test Results

In an untreated drill, regrinding of the cutting-edges was needed due tochipping when 500 holes had been bored, however the drill treatedaccording to the method of the present invention was able to bore up to1300 holes without performing regrinding, enabling the lifespan of thedrill to be greatly extended.

Moreover, holes formed using the drill of Example 3 were confirmed tohave improved smoothness of inner peripheral faces compared to cases inwhich the untreated drill was employed.

Moreover, in the example in which ejection particles were ejected underthe processing conditions of Comparative Example 3, the lifespan of thedrill was shortened by the occurrence of chipping compared to anuntreated drill.

The above results are thought to arise because, in cases employingejection particles made from a ceramic of lower toughness than ejectionparticles made of metal, considerable damage is imparted to the surfaceof the treatment subject compared to cases employing ejection particlesmade from metal.

These results are thought to show that even in cases employing the sameejection particles of 1000 HV, different results are obtained for thesame treatment subject in cases (Examples 1, 2) employing ejectionparticles made from metal (high-speed steel), to cases (ComparativeExample 3) employing the ejection particles are made from ceramic(zirconia-silica).

Thus in cases employing ejection particles made from a ceramic,preferably employed ejection particles have a hardness of not more than792 HV (approximately 800 HV) such as those for which the advantageouseffect of strengthening the binder metal phase (Co phase) is confirmedin the Example.

Test Example 4: Cylinder Inner Diameter Turning Insert (Cermet) (1) TestMethod

Ejection particles were ejected under the conditions listed in Table 6below against a diamond shaped insert made from a TiCN—NbC—Ni cermet(93HRA (1900 HV)) for turning the inner diameter of a cylinder made fromSUS304.

Note that the hardness of the Ni phase that is the binder metal phase isapproximately 500 HV.

TABLE 6 Treatment Conditions Example 4 Blasting Device Fine powdersuction type Ejection Material Glass particles Hardness 565 HV Averageparticle Approximately diameter 38 μm Shape Substantially sphericalshaped Ejection Pressure 0.4 MPa conditions Nozzle diameter 7 mmdiameter - long Ejection distance 100 mm Ejection duration Approximately1 second on each cutting-edge (each corner of diamond shaped insert)

The state of the surface of the insert was observed with the naked eyeafter ejection of the ejection particles under the conditions of Example4. An un-processed insert and the insert of Example 4 were each employedto turn the inner diameter of cylinders made from SUS304.

(2) Test Results

The surface of the cutting-edge portions of the untreated insert wassmooth, and the cutting-edges of the insert after treatment under thetreatment conditions of Example 4 was a slight matt finish. Thisconfirmed that ejection of the ejection particles enables plasticdeformation to be induced in the cutting-edge surfaces of the insert.

Moreover, although a lifespan of 1000 cycles of cylinder processing wasachieved with the untreated insert, 3000 cylinders could be processedwith the insert whose Ni phase had been strengthened by the treatmentconditions of Example 4, greatly increasing the lifespan by a multipleof three.

Moreover, the finish on the inner diameter finished surface was betteron cylinders machined using the insert of Example 4 than on cylindersmachined using the untreated insert.

For the WC—Co cemented carbide illustrated in Table 1, when glass beadsof 565 HV were employed as the ejection particles in Comparative Example1, the binder metal phase (Co phase) was not able to be strengthened dueto the hardness of the binder metal phase (Co phase) being 700 HV.However, in the Example 4 in which the treatment subject was theTiCN—NbC—Ni cermet having a binder metal phase (Ni phase) ofapproximately 500 HV, a greatly increased lifespan was obtained byemploying such glass beads of 565 HV as the ejection particles. Thepresent test results have been able to confirm that the lower limit to ahardness of the ejection particles capable of strengthening the bindermetal phase is decided in relation to the hardness of the binder metalphase.

Test Example 5: TiC Coated Cutting Insert (Carbide) (1) Test Method

Ejection particles were ejected under the conditions listed in Table 7below against a diamond shaped cutting insert made from a WC—TiC—TaC—Cocemented carbide (91.5HRA (1600 HV)) that had been coated with a TiCfilm at a film thickness of approximately 3 μm using a CVD method.

Note that the hardness of the Co phase that is the binder metal phase isapproximately 700 HV.

TABLE 7 Treatment Conditions Example 5 Blasting Device Fine powdersuction type Ejection Material Alumina-silica particles Hardness 792 HV(Approximately 800 HV) Average particle Approximately diameter 38 μmShape Substantially spherical shaped Ejection Pressure 0.4 MPaconditions Nozzle diameter 7 mm diameter - long Ejection distance 100 mmEjection duration Approximately 1 second on each cutting-edge (eachcorner of diamond shaped insert)

Compressive residual stress values were measured in the vicinity of thesurface of an untreated insert and an insert on to which ejectionparticles had been ejected under the conditions of Example 5. Each ofthe insert was also employed to machine a shaft made from SCM440.

(2) Test Results

The results of the above tests are illustrated in Table 8.

TABLE 8 Example 5 Untreated Residual stress at 5 μm from −1050 MPa +130MPa base material surface Number of shafts machined 120 shafts 60 shafts(lifespan)

(3) Interpretation

With the untreated insert, the TiC coating detached when 60 shafts hadbeen machined, and a replacement was needed due to chipping occurring inthe base material made from cemented carbide. However, with the inserttreated as Example 5, detachment of the TiC film was prevented, enabling120 shafts to be machined and greatly increasing the lifespan.

Such an increase in the cohesion strength of the TiC film is thought tobe obtained by the increased toughness of the cemented carbide servingas the base material.

Moreover, in the results of measurements of compressive residual stressvalues for the residual stress at a position 5 μm from the base materialsurface, although a tensile stress (+130 MPa) remained in the untreatedcase, which is thought to arise from heating when forming the TiC filmusing CVD, this changed to a compressive stress (−1050 MPa) when thetreatment of Example 5 had been performed thereon.

These results have confirmed that employing the method of the presentinvention enables the mechanical characteristics of the sintered bodybase material in a layer below the hard coating film to be changedwithout causing the hard coating film etc. to detach, even in cases inwhich a sintered body coated with a hard coating film such as TiC is thetreatment subject.

Note that in Example 5, even with the TiC coating film formed to a filmthickness of 3 μm, compressive residual stress was confirmed to beimparted to at least a depth of 5 μm in the base material below (a totaldepth of 8 μm when the 3 μm thickness of the hard coating film isincluded).

Thus the logical inference therefrom is that if the hard coating filmformed on the surface had a film thickness of up to about 5 μm, thencompressive residual stress can be imparted at least to a depth of about3 μm from the base material surface (a total depth of 8 μm when the 5 μmthickness of the hard coating film is included), and the binder metalphase in the vicinity of the surface of the sintered body can bestrengthened.

Test Example 6: Cutting Insert (cBN) (1) Test Method

Ejection particles were ejected under the conditions listed in Table 9below against a diamond shaped cutting insert made from cBN (4700 HV)configured from cubic crystals of boron nitride sintered together with aCo binder.

Note that in the cBN that has been sintered under ultrahigh pressure,the hardness of the Co phase binder is higher than in a carbide tool,and the hardness of the Co phase in the cBN of the present Test Exampleis approximately 800 HV.

TABLE 9 Treatment Conditions Example 6 Comparative Example 6 BlastingDevice Gravity type Gravity type Ejection Material HSS(SKH)Alumina-silica particles Hardness Approximately 1000 HV 792 HV Averageparticle Approximately Approximately diameter 40 μm 38 μm ShapeSubstantially Substantially spherical shaped spherical shaped EjectionPressure 0.4 MPa 0.4 MPa conditions Nozzle 9 mm diameter - 9 mmdiameter - diameter long long Ejection 100 mm 100 mm distance EjectionApproximately 1 second Approximately 1 second duration from each of 4directions from each of 4 directions at each cutting-edge at eachcutting-edge (each acute angled (each acute angled corner of diamondcorner of diamond shaped insert) shaped insert)

An untreated insert, and the inserts treated under the conditions ofExample 6 and Comparative Example 6 were each employed to machine shaftsof carburized and quenched steel, and the differences in lifespantherebetween confirmed.

(2) Test Results

The results of the above tests were then that whereas an untreatedinsert has a lifespan of machining 200 carburized and quenched shafts,the insert against which ejection particles had been ejected under theconditions of Example 6 was able to machine double that amount at 400carburized and quenched shafts.

The above results have confirmed that strengthening of the binder metalphase can be performed not only for a cemented carbide and cermet, butalso for cBN. A logical inference therefrom is that the method of thepresent invention applicable to sintered bodies in general that have astructure in which hard particles are bonded together by a binder metalphase.

Note that although strengthening of the Co phase could be performed byemploying ejection particles that were alumina-silica beads of 792 HV inExample 3, in which a drill made from a cemented carbide is thetreatment subject, an increased lifespan was not achieved for a sinteredbody having the same Co binder metal as the treatment subject in theComparative Example 6, in which a sintered body of cBN is the treatmentsubject, even when ejection particles of alumina-silica beads at 792 HVwere ejected thereon, and strengthening of the Co phase could not beachieved.

Such a difference is thought to be due to the cBN being sintered underultrahigh pressure as described above, making the hardness of the Cophase, at about 800 HV, about 100 HV higher than in a cemented carbidesuch that sufficient plastic deformation could not be imparted to the Cophase by alumina-silica beads of 792 HV. This is thought to result innot being able to achieve strengthening through work hardening frommicronization of the crystal structure and imparting compressiveresidual stress.

The present tests have accordingly confirmed that even in cases in whichthe metal employed as the material for the binder is the same, if thehardness of the binder metal phase is different due to differences inthe sintering conditions or the like, then there is a need to selectejection particles to match the relevant hardness.

Thus, the broadest claims that follow are not directed to a machine thatis configured in a specific way. Instead, said broadest claims areintended to protect the heart or essence of this breakthrough invention.This invention is clearly new and useful. Moreover, it was not obviousto those of ordinary skill in the art at the time it was made, in viewof the prior art when considered as a whole.

Moreover, in view of the revolutionary nature of this invention, it isclearly a pioneering invention. As such, the claims that follow areentitled to very broad interpretation so as to protect the heart of thisinvention, as a matter of law.

It will thus be seen that the objects set forth above, and those madeapparent from the foregoing description, are efficiently attained andsince certain changes may be made in the above construction withoutdeparting from the scope of the invention, it is intended that allmatters contained in the foregoing description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Now that the invention has been described;

DESCRIPTION OF REFERENCE NUMERALS

1 Sintered body (cemented carbide)

10 Hard particles

20 Binder metal phase

30 Spherical shaped ejection particles

1. A method of strengthening a binder metal phase of a sintered body,the binder metal phase strengthening method comprising: ejectingspherical shaped ejection particles against a surface of a sintered bodythat includes hard particles and a binder metal phase bonding the hardparticles together, by ejecting the spherical shaped ejection particlestogether with a compressed gas at an ejection pressure of from 0.2 MPato 0.6 MPa or at an ejection velocity of from 80 m/s to 200 m/s and thespherical ejection particles having a hardness that is not less than thehardness of the binder metal phase and that is a hardness of not morethan 1000 HV and being particles of from 100 grit to 800 grit, having anaverage particle diameter of from 20 μm to 149 μm.
 2. The sintered bodybinder metal phase strengthening method of claim 1, wherein a sinteredbody employed as a treatment subject is a sintered body having a hardcoating film coated on at least a portion of surface at a thickness ofnot more than 5 μm, and the ejection particles are ejected against thesintered body at the portion of the surface coated with the hard coatingfilm.
 3. The sintered body binder metal phase strengthening method ofclaim 1, wherein the ejection particles are metal particles, ceramicparticles, or a mixture of metal particles and ceramic particles.
 4. Thesintered body binder metal phase strengthening method of claim 1,wherein a hardness of the ceramic particles employed is not more than800 HV.
 5. The sintered body binder metal phase strengthening method ofclaim 2, wherein the ejection particles are metal particles, ceramicparticles, or a mixture of metal particles and ceramic particles.
 6. Thesintered body binder metal phase strengthening method of claim 2,wherein a hardness of the ceramic particles employed is not more than800 HV.
 7. The sintered body binder metal phase strengthening method ofclaim 3, wherein a hardness of the ceramic particles employed is notmore than 800 HV.
 8. The sintered body binder metal phase strengtheningmethod of claim 5, wherein a hardness of the ceramic particles employedis not more than 800 HV.